1. [Field of the Invention]
This invention relates to a method for detecting abnormalities in a crank angle sensor that generates a reference angle signal for each reference angle according to a the revolution of an internal combustion engine, and to an apparatus for detecting such abnormalities.
2. [Prior Art]
Japanese Laid-open Patent Application No. 6-81706 discloses an apparatus for detecting abnormalities in a crank angle sensor of the prior art.
As shown in FIG. 7, this apparatus comprises an air volume sensor 1 for detecting an amount of intake air, a crank angle sensor 2 for generating a reference angle signal for each reference angle according to the revolution of an internal combustion engine, and a control unit 10 that includes means 11 for detecting abnormalities in the crank angle sensor and flow detection means 12 for determining whether the engine is running, and detects abnormalities in the crank angle sensor based on outputs from these sensors.
A description is subsequently given of the operation of the apparatus as follows.
When a starter switch is turned on, a starter rotates, and the internal combustion engine starts revolving. At this time, an output of the air volume sensor 1, as shown in FIG. 8, changes from an initial state value C when the engine is not operating to a normal output value when air is absorbed by the revolution of the engine. At this point, the flow detection means 12 for detecting the amount of intake air judges that the engine is definitely running when an output value from the air volume sensor 1 is larger than a predetermined value X (which is set larger than the initial state value C and smaller than the minimum output value B at the time of cranking). If the flow detection means 12 judges that the engine is definitely running, the routine proceeds to the detection of abnormalities in the crank angle sensor. If the crank angle sensor 2 is in good order, a crank angle pulse corresponding to a predetermined crank angle is applied to the means 11 for detecting abnormalities in the crank angle sensor, which then judges that the crank angle sensor is in good order. However, if the crank angle sensor is out of order, the crank angle pulse is not applied to the means 11 for detecting abnormalities in the crank angle sensor. Instances in which a crank angle pulse is not detected on a temporary basis due to a short break caused by some reason or are taken into account in the prior art apparatus. If a crank angle pulse is not detected, the crank angle sensor is not immediately judged to be out of order, but if a crank angle pulse is not detected for a predetermined interval (an elapsed time 2 of one second, for example), the crank angle sensor is judged to be out of order.
In the above apparatus of the prior art, the predetermined value X, which is a decision value for the means 12 for detecting the amount of intake air, must be set within the range that satisfies value C&lt;predetermined value X&lt;value B. However, the difference between value C and value B is generally small (about 0.4 V or less) as shown in FIG. 9. Moreover, the output of the sensor is affected by the temperature and density of intake air, supply voltage and other factors, and errors are caused by differences among mass-produced sensors. It is therefore generally difficult to set a predetermined value that is between value C and value B.
When the electromotive force of the battery falls at low temperatures or when the battery is weak, the waveform shown in FIG. 10 is obtained as an output of the air volume sensor when a starter is rotated and the engine starts cranking. In this case, as is evident from FIG. 10, since value C.gtoreq.value B, it is impossible to set a predetermined value X that is larger than value C and smaller than value B. Even when the predetermined value is set to any value larger than value C, detection is omitted. In other words, since the predetermined value cannot be set smaller than value C, a value of the output waveform is smaller than the predetermined value within the trough of the output waveform of FIG. 10. Therefore, a timer for counting the elapsed time 2 is reset each time a trough appears in the output waveform and detection of abnormalities is never carried out, i.e., detection is omitted.
When the engine operates during a drive, and then stops for some reason or another, there is a residual negative pressure in the duct or the like. Therefore, though the engine stops, air is sucked in until the negative pressure disappears. The result, as shown in FIG. 11, is the generation of a signal indicating the erroneous existence of air flow by the air volume sensor. Thereby, erroneous abnormality detection is made. In other words, in the prior art, if an output value of the air volume sensor 1 is larger than the predetermined value X, the engine is judged to be definitely running and the routine proceeds to the detection of abnormalities in the crank angle sensor 2. Therefore, when the engine stops and an output of the air volume sensor 1 is higher than the predetermined value X due to the existence of negative pressure, the routine for detecting abnormalities in the crank angle sensor 2 is initiated, and the detection is made according to the presence or absence of an output from the crank angle sensor 2. At this point, since there is no output from the crank angle sensor 2, the crank angle sensor 2 is judged to be out of order even when it is not.
In the end, the apparatus for detecting abnormalities in a crank angle sensor of the prior art suffers from low reliability. For example, when the engine stops during a drive, the crank angle sensor is improperly judged to be out of order even when the sensor is actually in good order (erroneous detection), or when the temperature is low or the battery weak, the apparatus cannot detect abnormalities (detection omission).